The presence of pathogens in blood products, as well as other biological materials, is recognized as a significant health problem to health workers as well as recipients of the materials.
With regard to health workers, a great volume of human fluids is handled daily as part of the routine monitoring of hospital patients by obtaining and testing human fluids (blood, urine, spinal fluid, etc.). Typically, each admitted patient has at least a tube of blood collected every day by a phlebotomist. During the transferring, portioning and testing process, each sample tube is handled by at a clinical worker while its contents are exposed. This intensive handling of potentially infectious human fluids is not without health risk. The Occupational Safety and Health Administration (OSHA) estimates that over five million health workers, including hospital laboratory workers, are exposed to blood borne-pathogen infections in the work place annually. The pathogen responsible for the overwhelming majority of infections is the hepatitis B virus (HBV). The Center for Disease Control (CDC) estimates there are twelve thousand cases of HBV infection among health workers each year. Of these cases, over five hundred require hospitalization and approximately two hundred and fifty of these patients die (i.e. from fulminant hepatitis, cirrhosis or liver cancer). See Guidelines for Prevention of Transmission of HIV and HBV to Health-Care and Public Safety Workers, CDC (February 1989). Most full time laboratory employees contract hepatitis at least once during their career. Indeed, up to one third of all health care workers show serological evidence of a previous HBV infection. Id.
Following the recognition of Acquired Immunodeficiency Syndrome (AIDS), clinical laboratories have instituted additional precautions. For example, rather than using manually positioned plastic inserts to maintain the separation of cells from serum after samples are centrifuged, a "gel" is now available that is in the empty tube at the time the blood is drawn. When the tube is centrifuged the cells go below the gel while the serum remains above. While the separation can be maintained in this manner without as much sample handling, this does not reduce the handling of the technologist at the point of analysis. Unfortunately, infectious virus can persist in a liquid or dried state for prolonged periods of time, possibly even at elevated temperatures. Resnick et al., JAMA 255:1887 (1986).
Preventative measures such as gloves and eye-wear are not complete solutions to the problem. Accidents in the laboratory or clinic typically involve exposure over a larger portion of the body and disease can be transmitted through the skin and mucous membranes. Morbidity and Mortality Weekly Report 36:285 (1987).
Clearly, there remains a need for a more adequate solution to blood borne-pathogen infections in the work place. Such a solution should serve as a protection against a wide range of pathogens. Furthermore, the mechanics of the solution should not unduly interfere with operations of a laboratory or blood bank.
Another significant problem is the contamination of the blood supply for in vivo use. The safety of the blood supply continues to be threatened by the transmission of pathogens by transfusion. While the threat posed by the human immunodeficiency virus (HIV) and the Acquired Immune Deficiency Syndrome (AIDS) is now widely publicized, contamination of blood products with a number of other blood-borne infectious viral agents is of even greater concern. See R. Y. Dodd, In: Transfusion Medicine in the 1990's (American Assoc. Blood Banks 1990) (S. J. Nance, ed.). For example, in the United States, it is estimated that up to ten (10) percent of multiply transfused recipients develop hepatitis accounting for many thousands of cases annually.
Whole blood collected from volunteer donors for transfusion recipients is typically separated into its components: red blood cells, platelets, and plasma. Each of these fractions are individually stored and used to treat a multiplicity of specific conditions and disease states.
The red blood cell component is used primarily to treat trauma, chronic anemia, and blood loss due to surgery (particularly cardiac and liver surgery), including postoperative bleeding. D. M. Surgenor et al. Transfusion 32:458 (1992). Approximately twelve (12) million units of red cells are transfused into approximately four (4) million recipients annually in the United States alone. E. L. Wallace et al. Transfusion 33:139 (1993).
The safety of the blood supply cannot be assured by merely testing the blood for pathogens before transfusion. Most testing relies on the detection of antibodies to the pathogen in the prospective blood donor. It is now well-documented that infectious agents can be transmitted by "seronegative" blood donors, i.e. donors that have no detectable antibodies to the pathogen. For example, thirteen cases of transfusion-related AIDS have been reported to the Centers for Disease Control (CDC) among recipients of blood that was pre-tested and found negative for antibody to the HIV-1 virus.
Clerical errors and other mistakes further expose patients to contaminated, incorrectly tested or mislabeled blood. To complicate the problem, one bad unit can create several victims, since whole blood is routinely split into components. Mistakes are not infrequent in blood banks. Since the beginning of 1990, 29,586 blood bank errors and accidents have been reported to the FDA. "How Safe Is Our Blood," U.S. News and World Report, Jun. 27, 1994, 68-78. Recalls by blood centers of blood released in error are generally ineffective because they take place months or years after the blood products have been transfused.
An alternative approach to eliminate transmission of diseases through blood products is to develop a means to inactivate pathogens in transfusion products. Some of these techniques such as heat [J. Hilfenhous et al. J. Biol. Std. 70:589 (1987)], solvent/detergent treatment [B. Horowitz et al. Transfusion 25:516 (1985)], gama-irradiation [G. Moroff et al. Transfusion 26:453 (1986)] or UV alone [K. N. Proudouz et al. Blood 70:589 (1987)] are completely incompatible with maintenance of red cell function.
Another means to inactivate pathogens is the use of methylene blue. S. J. Wagner et al. examined methylene blue as a virucidal for red cell solutions. S. J. Wagner et al. Transfusion 33:30 (1993). Photo treatment of red cells with methylene blue was found to cause loss of ATP, enhanced ion permeability, and binding of autologous immunoglobulin (IgG) to the red cell surface. It was speculated that some general (and undesirable) modification of the red cell membrane occurs as a result of the treatment.
Yet another approach is to deplete the red cell product of contaminating lymphocytes which may harbor viral pathogens. Both leukodepletion with filters and freeze/thaw procedures have been examined. S. M. Bruisten et al. Transfusion 30:833 (1990). Complete removal of lymphocytes, however, cannot be achieved with such methods. Furthermore, leukodepletion does not address cell-free virus. Thus, this approach is not sufficient to render blood completely safe.
Finally, there is the approach of avoiding blood and using blood substitutes. Hemoglobin solutions, perfluorocarbon emulsions and vesicle-encapsulated hemoglobin have all been suggested as candidates. Unfortunately, each of these has been shown to be inadequate as a general substitute. See R. M. Winslow In: Blood Safety: Current Challenges (S. J. Nance ed.) (AABB 1992) (pp. 151-167).
In sum, there is a need for a means of inactivating viral pathogens in red blood cell solutions. This approach must be effective without causing harm to the blood product or the transfusion recipient.